The average of 3, 15, and my number is 40. What is my number?

102

Step-by-step explanation:

Let your number be n

The average of 3,15 and your number is found by adding the three numbers and dividing by 3

(3+15+n) / 3

That is equal to 40

(3+15+n) / 3=40

Multiply each side by 3 to get rid of the fraction

(3+15+n) / 3 * 3 = 40*3

(3+15+n) = 120

Combine like terms

18+n = 120

Subtract 18 from each side

18-18 + n = 120-18

n = 102

Your number is 102

Answer: the average of 3 and 15 is 9